Liquid solder resist composition and covered-printed wiring board

ABSTRACT

A liquid solder resist composition contains a carboxyl group-containing resin, a photopolymerizable compound containing at least one compound selected from a group consisting of a photopolymerizable monomer and a photopolymerizable prepolymer, a photopolymerization initiator, a titanium dioxide, and a compound having a cyclic ether skeleton. The titanium dioxide contains both of a rutile titanium dioxide manufactured by a sulfuric acid method and a rutile titanium dioxide manufactured by a chlorine method.

TECHNICAL FIELD

The present invention relates to a liquid solder resist composition and a covered-printed wiring board, and specifically relates to a liquid solder resist composition that has photocurability and can be developed using an alkaline solution, and a covered-printed wiring board that includes a solder resist layer made of the liquid solder resist composition.

BACKGROUND ART

In recent years, as a method for forming solder resist layers on printed-wiring boards for consumer use and industrial use, a method using a liquid solder resist composition that has excellent resolution, size precision, and the like, and can be developed has been widely adopted, instead of a screen printing method, in order to increase the density of wiring on the printed-wiring board.

Also, in recent years, optical elements such as light-emitting diodes are often mounted directly on a printed-wiring board on which a solder resist layer is formed to cover the printed-wiring board, for uses in: backlights of liquid crystal displays of mobile terminals, personal computers, televisions, and the like; light sources of illumination devices; and the like. Furthermore, as a result of the solder resist layer of the printed-wiring board on which optical elements are mounted containing titanium dioxide, the solder resist layer is whitened, which allows light emitted from light-emitting elements to efficiently reflect off the solder resist layer (see JP2011-17010A, JP4657358B, JP2011-215384A).

SUMMARY OF INVENTION

There exist two kinds of titanium dioxides depending on manufacturing methods such as a sulfuric acid method (liquid phase method) and a chlorine method (gas phase method). There also exist other two kinds of titanium dioxides, which are a rutile titanium dioxide and an anatase titanium dioxide, depending on crystal structure.

However, there is a problem that a solder resist layer containing the rutile titanium dioxide manufactured by the sulfuric acid method has low light reflectivity even though it has less deterioration due to ultraviolet rays and heat.

Also, there are problems that, even though a solder resist layer containing the rutile titanium dioxide manufactured by the chlorine method has high reflectivity, the light reflectivity decreased due to ultraviolet rays irradiation and thus it is difficult to maintain the high reflectivity and the solder resist layer easily turns its color to yellow due to ultraviolet rays.

Furthermore, there is a problem that a solder resist layer containing the anatase titanium dioxide is originally not white but yellowish, has large deterioration of a coating film due to ultraviolet rays and heat, and has low light reflectivity.

The present invention has been made in light of the above-described circumstances, and it is an object thereof to provide a liquid solder resist composition capable of forming a solder resist layer that has high reflectivity with suppressed deterioration especially due to light, and to provide a covered-printed wiring board including a solder resist layer made of the liquid solder resist composition.

The liquid solder resist composition according to the present invention includes a carboxyl group-containing resin, a photopolymerizable compound containing at least one compound selected from a group consisting of a photopolymerizable monomer and a photopolymerizable prepolymer, a photopolymerization initiator, a titanium dioxide, and a compound having a cyclic ether skeleton, and the titanium dioxide contains both of a rutile titanium dioxide manufactured by a sulfuric acid method and a rutile titanium dioxide manufactured by a chlorine method.

The covered-printed wiring board according to the present invention includes a printed-wiring board and a solder resist layer that covers the printed-wiring board, and the solder resist layer is made of the above-described liquid solder resist composition.

DESCRIPTION OF EMBODIMENTS

An embodiment for implementing the present invention will now be described.

A liquid solder resist composition according to this embodiment contains a carboxyl group-containing resin, a photopolymerizable compound, a photopolymerization initiator, a titanium dioxide, and a compound having a cyclic ether skeleton. Each of the components is described further in detain hereinafter. It should be noted that in the present invention, “(meth)acryl” means at least one selected from “acryl” and “methacryl” and “(meth)acrylate” means at least one selected from “acrylate” and “methacrylate”.

The carboxyl group-containing resin can provide the coating film made of the liquid solder resist composition with a capability of being developed using an alkaline solution, or in other words, with an alkaline development capability.

The carboxyl group-containing resin can contain a compound that has a carboxyl group and that is not photopolymerizable (hereinafter, referred to as (A1) component).

The (A1) component contains, for example, polymer of an ethylene-based unsaturated monomer that contains an ethylene-based unsaturated compound having a carboxyl group. Furthermore, the ethylene-based unsaturated monomer may contain an ethylene-based unsaturated compound that does not have a carboxyl group.

The ethylene-based unsaturated compound having a carboxyl group can contain an appropriate polymer and prepolymer, and for example, can contain a compound that has only one ethylene-based unsaturated group. More specifically, for example, the ethylene-based unsaturated compound having a carboxyl group can contain at least one compound selected from the group consisting of acrylic acid, methacrylic acid, ω-carboxy-polycaprolactone (n≈2) monoacrylate, crotonic acid, cinnamic acid, 2-acryloyloxyethyl succinate, 2-methacryloyloxyethyl succinate, 2-acryloyloxyethyl phthalate, 2-methacryloyloxyethyl phthalate, 2-acryloyloxypropyl phthalate, 2-methacryloyloxypropyl phthalate, 2-acryloyloxyethyl maleate, 2-methacryloyloxyethyl maleate, β-carboxyethyl acrylate, 2-acryloyloxyethyl tetrahydrophthalate, 2-methacryloyloxyethyl tetrahydrophthalate, 2-acryloyloxyethyl hexahydrophthalate, and 2-methacryloyloxyethyl hexahydrophthalate. The ethylene-based unsaturated compound having a carboxyl group can also contain a compound having a plurality of ethylene-based unsaturated groups. More specifically, for example, the ethylene-based unsaturated compound having a carboxyl group can contain a compound obtained by causing polyfunctional (meth)acrylate having a hydroxyl group selected from the group consisting of pentaerythritol triacrylate, pentaerythritol trimethacrylate, trimethylolpropane diacrylate, trimethylolpropane dimethacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol pentamethacrylate to react with a dibasic acid anhydride. These compounds are used alone or in combination.

It is sufficient that the ethylene-based unsaturated compound that does not have a carboxyl group is a compound that is able to be copolymerized with an ethylene-based unsaturated compound having a carboxyl group. The ethylene-based unsaturated compound that does not have a carboxyl group can contain a compound that has an aromatic ring and/or a compound that does not have an aromatic ring.

The compound that has an aromatic ring can contain at least one compound selected from the group consisting of 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalate, benzyl (meth)acrylate, neopentyl glycol benzoate (meth)acrylate, paracumylphenoxyethylene glycol (meth)acrylate, EO-modified cresol (meth)acrylate, ethoxylated phenyl (meth)acrylate, nonylphenoxy polyethylene glycol (meth)acrylate (n=2 to 17), ECH-modified phenoxy (meth)acrylate, phenoxy diethylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxy hexaethylene glycol (meth)acrylate, phenoxy tetraethylene glycol (meth)acrylate, tribromophenyl (meth)acrylate, EO-modified tribromophenyl (meth)acrylate, EO-modified bisphenol A di(meth)acrylate, PO-modified bisphenol A di(meth)acrylate, modified bisphenol A di(meth)acrylate, EO-modified bisphenol F di(meth)acrylate, ECH-modified phthalic acid di(meth)acrylate, trimethylolpropane benzoate (meth)acrylate, EO-modified phthalic acid (meth)acrylate, EO/PO-modified phthalic acid (meth)acrylate, N-phenylmaleimide, N-benzylmaleimide, N-vinylcarbazole, styrene, vinylnaphthalene, and 4-vinylbiphenyl, for example.

The compound that does not have an aromatic ring can contain at least one compound selected from the group consisting of linear or branched aliphatic or alicyclic (which may include a ring having an unsaturated bond) (meth)acrylic acid esters, hydroxyalkyl (meth)acrylates, and alkoxyalkyl (meth)acrylates, and N-substituted maleimides such as N-cyclohexylmaleimide, for example. The compound that does not have an aromatic ring may contain a compound having two or more ethylene-based unsaturated groups in one molecule, such as polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate. These compounds are used alone or in combination. These compounds are preferable in that the hardness and oiliness of the solder resist layer are easily adjusted.

Types, ratios, and the like of a compound used to obtain the (A1) component are appropriately selected such that the acid value of the (A1) component has an appropriate value. The acid value of the (A1) component is preferably within a range of 20 to 180 mgKOH/g, and more preferably within a range of 35 to 165 mgKOH/g.

The carboxyl group-containing resin can also contain a photopolymerizable carboxyl group-containing resin (hereinafter, referred to as a (A2) component) having a carboxyl group and a photopolymerizable functional group. The photopolymerizable functional group is an ethylene-based unsaturated group, for example.

The (A2) component can contain, for example, a resin (hereinafter, referred to as a first resin (a)) having a structure obtained by: at least one of epoxy groups in an epoxy compound (a1) having two or more epoxy groups in one molecule being reacted with an ethylene-based unsaturated compound (a2) having a carboxyl group; and at least one compound (a3) selected from a group consisting of polyvalent carboxylic acids and anhydrides thereof being further added to the reaction product.

The epoxy compound (a1) can contain at least one compound selected from the group consisting of cresol novolac epoxy resins, phenol novolac epoxy resins, bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol A-novolac epoxy resins, naphthalene epoxy resins, biphenyl epoxy resins, biphenyl aralkyl epoxy resins, triglycidyl isocyanurate, alicyclic epoxy resins, and a polymer of an ethylene-based unsaturated compound containing a compound having an epoxy group, for example.

The epoxy compound (a1) may contain the polymer of the ethylene-based unsaturated compound (p) containing the compound (p1) having an epoxy group. The ethylene-based unsaturated compound (p) that is provided in the synthesis of this polymer may only contain the compound (p1) having an epoxy group, or may contain the compound (p1) having an epoxy group and a compound (p2) that does not have an epoxy group.

The compound (p1) having an epoxy group can contain a compound selected from appropriate polymers and prepolymers. Specifically, the compound (p1) having an epoxy group can contain at least one compound selected from the group consisting of epoxycyclohexyl derivatives of acrylic acid, epoxycyclohexyl derivatives of methacrylic acid, alicyclic epoxy derivatives of acrylate, alicyclic epoxy derivatives of methacrylate, β-methylglycidyl acrylate, and β-methylglycidyl methacrylate. In particular, it is preferable that the compound (p1) having an epoxy group contains glycidyl (meth)acrylate that is generally used and can be easily obtained.

It is sufficient that the compound (p2) that does not have an epoxy group is a compound that can copolymerize with the compound (p1) having an epoxy group. The compound (p2) that does not have an epoxy group can contain at least one compound selected from the group consisting of 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalate, 2-(meth)acryloyloxypropyl phthalate, benzyl (meth)acrylate, neopentyl glycol benzoate (meth)acrylate, paracumylphenoxyethylene glycol (meth)acrylate, EO-modified cresol (meth)acrylate, ethoxylated phenyl (meth)acrylate, nonylphenoxy polyethylene glycol (meth)acrylate (degree of polymerization n=2 to 17), ECH-modified phenoxy (meth)acrylate, phenoxy diethylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxy hexaethylene glycol (meth)acrylate, phenoxy tetraethylene glycol (meth)acrylate, tribromophenyl (meth)acrylate, EO-modified tribromophenyl (meth)acrylate, EO-modified bisphenol A di(meth)acrylate, PO-modified bisphenol A di(meth)acrylate, modified bisphenol A di(meth)acrylate, EO-modified bisphenol F di(meth)acrylate, ECH-modified phthalic acid di(meth)acrylate, trimethylolpropane benzoate (meth)acrylate, EO-modified phthalic acid (meth)acrylate, EO/PO-modified phthalic acid (meth)acrylate, vinylcarbazole, styrene, N-phenylmaleimide, N-benzylmaleimide, 3-maleimide benzoic acid N-succinimidyl, linear or branched aliphatic or alicyclic (which may include a ring having an unsaturated bond) (meth)acrylic acid esters, hydroxyalkyl (meth)acrylate, alkoxyalkyl (meth)acrylate, and N-substituted maleimides (for example, N-cyclohexylmaleimide), for example.

The compound (p2) that does not have an epoxy group may contain a compound having two or more ethylene-based unsaturated groups in one molecule. As a result of this compound being used and the amount thereof being adjusted, the hardness and oiliness of the solder resist layer is easily adjusted. The compound having two or more ethylene-based unsaturated groups in one molecule can contain at least one compound selected from the group consisting of polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate, for example.

Polymers can be obtained by the ethylene-based unsaturated compound (p) being polymerized by a known polymerization method such as a solution polymerization method or an emulsion polymerization method, for example. Specific examples of solution polymerization methods include a method in which the ethylene-based unsaturated compound (p) is heated and stirred in an appropriate organic solvent with a polymerization initiator under a nitrogen atmosphere, and an azeotropic polymerization method.

An organic solvent used for polymerization of the ethylene-based unsaturated compound (p) can contain at least one compound selected from the group consisting of ketones such as methylethyl ketone and cyclohexanone, aromatic hydrocarbons such as toluene and xylene, acetate esters such as ethyl acetate, butyl acetate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, and propylene glycol monomethyl ether acetate, and dialkylglycol ethers, for example.

The polymerization initiator used for polymerization of the ethylene-based unsaturated compound (p) can contain at least one compound selected from the group consisting of hydroperoxides such as diisopropyl benzene hydroperoxide, dialkyl peroxides such as dicumyl peroxide and 2,5-dimethyl-2,5-di-(t-butylperoxy)-hexane, diacyl peroxides such as isobutyryl peroxide, ketone peroxides such as methyl ethyl ketone peroxide, alkyl peresters such as t-butyl peroxypivalate, peroxydicarbonates such as diisopropyl peroxydicarbonate, azo compounds such as azobisisobutyronitrile, and redox-system initiators, for example.

The ethylene-based unsaturated compound (a2) can contain a compound selected from the group consisting of appropriate polymers and prepolymers. The ethylene-based unsaturated compound (a2) can contain a compound having only one ethylene-based unsaturated group. The compound having only one ethylene-based unsaturated group can contain at least one compound selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, 2-acryloyloxyethyl succinate, 2-methacryloyloxyethyl succinate, 2-acryloyloxyethyl phthalate, 2-methacryloyloxyethyl phthalate, β-carboxyethyl acrylate, 2-acryloyloxyethyl tetrahydrophthalate, 2-methacryloyloxyethyl tetrahydrophthalate, 2-acryloyloxyethyl hexahydrophthalate, and 2-methacryloyloxyethyl hexahydrophthalate, for example. The ethylene-based unsaturated compound (a2) can contain a compound having a plurality of ethylene-based unsaturated groups. The compound having the plurality of ethylene-based unsaturated groups can contain at least one compound selected from the group consisting of compounds obtained by causing polyfunctional acrylates and polyfunctional methacrylates that have a hydroxyl group, such as pentaerythritol triacrylate, pentaerythritol trimethacrylate, trimethylolpropane diacrylate, trimethylolpropane dimethacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol pentamethacrylate to react with a dibasic acid anhydride, for example.

In particular, it is preferable that the ethylene-based unsaturated compound (a2) contains at least one of acrylic acid and methacrylic acid. In this case, the ethylene-based unsaturated group derived from acrylic acid and methacrylic acid has excellent photoreactivity in particular, and thus the first resin (a) has high photoreactivity.

The usage amount of the ethylene-based unsaturated compound (a2) is preferably within a range of 0.4 to 1.2 mol of the carboxyl group in the ethylene-based unsaturated compound (a2) relative to 1 mol of the epoxy group in the epoxy compound (a1), and preferably particularly within a range of 0.5 to 1.1 mol of the carboxyl group relative to 1 mol of the epoxy group.

The compound (a3) selected from the group consisting of polyvalent carboxylic acids and anhydrides thereof can contain at least one compound selected from the group consisting of dicarboxylic acids such as phthalic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, methylnadic acid, hexahydrophthalic acid, methyl hexahydrophthalic acid, succinic acid, methylsuccinic acid, maleic acid, citraconic acid, glutaric acid, and itaconic acid; polyvalent carboxylic acids of tribasic acids or greater polyvalent carboxylic acids such as cyclohexane-1,2,4-tricarboxylic acid, trimellitic acid, pyromellitic acid, benzophenone tetracarboxylic acid, and methylcyclohexene tetracarboxylic acid; and anhydrides of these polyvalent carboxylic acids.

The compound (a3) is used mainly for the purpose of giving an acid value to the first resin (a) so that the liquid solder resist composition re-disperses and re-dissolves in a dilute aqueous alkaline solution. The usage amount of the compound (a3) is adjusted such that the first resin (a) preferably has an acid value of 30 mgKOH/g or greater, and particularly preferably has an acid value of 60 mgKOH/g or greater. Also, the usage amount of the compound (a3) is adjusted such that the first resin (a) preferably has an acid value of 160 mgKOH/g or less, and particularly preferably 130 mgKOH/g or less.

When the first resin (a) is synthesized, a known method can be adopted to cause the addition reaction between the epoxy compound (a1) and the ethylene-based unsaturated compound (a2) and the addition reaction between the product resulting from this addition reaction (addition reaction product) and the compound (a3) to progress. For example, at the time of the addition reaction between the epoxy compound (a1) and the ethylene-based unsaturated compound (a2), the ethylene-based unsaturated compound (a2) is added to the solvent solution of the epoxy compound (a1), and a thermal polymerization inhibitor and a catalyst are further added as needed, and then the mixture is stirred and mixed to obtain a reactive solution. As a result of causing the reaction of this reactive solution using a usual method at a reaction temperature of preferably 60 to 150° C., and particularly preferably 80 to 120° C., the addition reaction product can be obtained. Examples of the thermal polymerization inhibitor include hydroquinone and hydroquinone monomethyl ether. Examples of the catalyst include tertiary amines such as benzyldimethylamine and triethylamine, quaternary ammonium salts such as trimethylbenzylammonium chloride and methyltriethylammonium chloride, triphenylphosphine, and triphenyl stibine.

When the addition reaction between the addition reaction product and the compound (a3) is caused to progress, the compound (a3) is added to the solvent solution containing the addition reaction product, a thermal polymerization inhibitor and a catalyst are further added as needed, and then the mixture is stirred and mixed to obtain a reactive solution. As a result of causing the reaction of the reactive solution using a usual method, the first resin (a) can be obtained. It is sufficient that reaction conditions are the same as those for the case of the addition reaction between the epoxy compound (a1) and the ethylene-based unsaturated compound (a2). The compounds used at the time of the addition reaction between the epoxy compound (a1) and the ethylene-based unsaturated compound (a2) having a carboxyl group can be used as is, as the thermal polymerization inhibitor and the catalyst.

The (A2) component may contain a carboxyl group-containing (meth)acryl-based copolymer resin (referred to as a second resin (b)) obtained by causing a portion of carboxyl groups in the polymer of an ethylene-based unsaturated monomer containing an ethylene-based unsaturated compound having a carboxyl group to react with an ethylene-based unsaturated compound having an epoxy group. The ethylene-based unsaturated monomer may also include an ethylene-based unsaturated compound that does not have a carboxyl group as needed.

The ethylene-based unsaturated compound having a carboxyl group for obtaining the second resin (b) can contain an appropriate polymer and/or prepolymer. For example, the ethylene-based unsaturated compound having a carboxyl group can contain a compound having only one ethylene-based unsaturated group. More specifically, the ethylene-based unsaturated compound having a carboxyl group can contain at least one compound selected from the group consisting of acrylic acid, methacrylic acid, ω-carboxy-polycaprolactone (n≈2) monoacrylate, crotonic acid, cinnamic acid, 2-acryloyloxyethyl succinate, 2-methacryloyloxyethyl succinate, 2-acryloyloxyethyl phthalate, 2-methacryloyloxyethyl phthalate, β-carboxyethyl acrylate, 2-acryloyloxypropyl phthalate, 2-methacryloyloxypropyl phthalate, 2-acryloyloxyethyl maleate, 2-methacryloyloxyethyl maleate, 2-acryloyloxyethyl tetrahydrophthalate, 2-methacryloyloxyethyl tetrahydrophthalate, 2-acryloyloxyethyl hexahydrophthalate, and 2-methacryloyloxyethyl hexahydrophthalate, for example. The ethylene-based unsaturated compound having a carboxyl group can contain a compound having a plurality of ethylene-based unsaturated groups. More specifically, for example, the ethylene-based unsaturated compound having a carboxyl group can contain a compound obtained by causing polyfunctional (meth)acrylate having a hydroxyl group selected from the group consisting of pentaerythritol triacrylate, pentaerythritol trimethacrylate, trimethylolpropane diacrylate, trimethylolpropane dimethacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol pentamethacrylate to react with a dibasic acid anhydride. These compounds are used alone or in combination.

It is sufficient that the ethylene-based unsaturated compound that does not have a carboxyl group for obtaining the second resin (b) is a compound that can copolymerize with the ethylene-based unsaturated compound having a carboxyl group. The ethylene-based unsaturated compound that does not have a carboxyl group can contain a compound that has an aromatic ring and/or a compound that does not have an aromatic ring.

The compound that has an aromatic ring can contain at least one compound selected from the group consisting of 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalate, benzyl (meth)acrylate, neopentyl glycol benzoate (meth)acrylate, paracumylphenoxyethylene glycol (meth)acrylate, EO-modified cresol (meth)acrylate, ethoxylated phenyl (meth)acrylate, nonylphenoxy polyethylene glycol (meth)acrylate (n=2 to 17), ECH-modified phenoxy (meth)acrylate, phenoxy diethylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxy hexaethylene glycol (meth)acrylate, phenoxy tetraethylene glycol (meth)acrylate, tribromophenyl (meth)acrylate, EO-modified tribromophenyl (meth)acrylate, EO-modified bisphenol A di(meth)acrylate, PO-modified bisphenol A di(meth)acrylate, modified bisphenol A di(meth)acrylate, EO-modified bisphenol F di(meth)acrylate, ECH-modified phthalic acid di(meth)acrylate, trimethylolpropane benzoate (meth)acrylate, EO-modified phthalic acid (meth)acrylate, EO/PO-modified phthalic acid (meth)acrylate, N-phenylmaleimide, N-benzylmaleimide, N-vinylcarbazole, styrene, vinylnaphthalene, and 4-vinylbiphenyl, for example.

The compound that does not have an aromatic ring can contain at least one compound selected from the group consisting of linear or branched aliphatic or alicyclic (which may include a ring having an unsaturated bond) (meth)acrylic acid esters, hydroxyalkyl (meth)acrylates, and alkoxyalkyl (meth)acrylates, and N-substituted maleimides such as N-cyclohexylmaleimide, for example. The compound that does not have an aromatic ring may contain a compound having two or more ethylene-based unsaturated groups in one molecule, such as polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate. These compounds are used alone or in combination. These compounds are preferable in that the hardness and oiliness of the solder resist layer are easily adjusted.

Examples of the ethylene-based unsaturated compound having an epoxy group for obtaining the second resin (b) include appropriate polymers and prepolymers. Specific examples of the ethylene-based unsaturated compound having an epoxy group include epoxycyclohexyl derivatives of acrylic acid or methacrylic acid; alicyclic epoxy derivatives of acrylate or methacrylate; β-methylglycidyl acrylate, and β-methylglycidyl methacrylate. These compounds are used alone or in combination. In particular, it is preferable to use glycidyl (meth)acrylate that is generally used and can be easily obtained.

The (A2) component may contain a resin (hereinafter, referred to as a third resin (c)) obtained by adding a compound having an ethylene-based unsaturated group and an isocyanate group to a portion or all of hydroxyl groups in a polymer of an ethylene-based unsaturated monomer that contains both an ethylene-based unsaturated compound having a carboxyl group and an ethylene-based unsaturated compound having a hydroxyl group. The ethylene-based unsaturated monomer may contain an ethylene-based unsaturated compound that does not have a carboxyl group nor hydroxyl group as needed.

Examples of the ethylene-based unsaturated compound having a carboxyl group for obtaining the third resin (c) may be the same as those recited for the ethylene-based unsaturated compound having a carboxyl group for obtaining the second resin (b) described above, for example.

Specific examples of the ethylene-based unsaturated compound having a hydroxyl group for obtaining the third resin (c) include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, cyclohexanedimethanol mono(meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxyethylphtalate, caprolactone (meth)acrylate, polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, trimethylolpropane di(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol penta(meth)acrylate; hydroxybutyl vinyl ether; hydroxyethyl vinyl ether, and N-hydroxyethyl (meth)acrylamide.

Specific examples of the compound having an ethylene-based unsaturated group and an isocyanate group for obtaining the third resin (c) include 2-acryloyloxyethyl isocyanate (specific examples include part number “Karenz AOI” (Showa Denko K.K.)), 2-methacryloyloxyethyl isocyanate (specific examples include part number “Karenz MOI” (Showa Denko K.K.)), methacryloyloxyethoxyethyl isocyanate (specific examples include part number “Karenz MOI-EG” (Showa Denko K.K.)), an isocyanate block body of Karenz MOI (specific examples include part number “Karenz MOI-BM” (Showa Denko K.K.)), an isocyanate block body of Karenz MOI (specific examples include part number “Karenz MOI-BP” (Showa Denko K.K.), and 1,1-(bisacryloyloxymethyl)ethyl isocyanate) (specific examples include part number “Karenz BEI” (Showa Denko K.K.)).

It is preferable that the weight average molecular weight of the (A2) component as a whole is within a range of 800 to 100000. In this range, a liquid solder resist composition can achieve excellent photosensitivity and resolution.

The acid value of the (A2) component as a whole is preferably 30 mgKOH/g or greater, and in this case, the liquid solder resist composition can be easily developed. It is further preferable that this acid value is 60 mgKOH/g or greater. Also, the acid value of the (A2) component as a whole is preferably 180 mgKOH/g or less, and in this case, a residual amount of carboxyl groups in a covering film made of the liquid solder resist composition is reduced, and good electrical properties, electrical corrosion-resistance, water-resistance, and the like of the covering film are maintained. It is further preferable that the acid value is 150 mgKOH/g or less.

A photopolymerizable compound provides the liquid solder resist composition with photocurability. The photopolymerizable compound contains at least one compound selected from the group consisting of photopolymerizable monomers and photopolymerizable prepolymers.

The photopolymerizable monomer has an ethylene-based unsaturated group, for example. The photopolymerizable monomer can contain at least one compound selected from the group consisting of monofunctional (meth)acrylates such as 2-hydroxyethyl (meth)acrylate; and polyfunctional (meth)acrylates such as diethylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and ε-caprolactone modified pentaerythritol hexaacrylate, for example.

It is also preferable that the photopolymerizable monomer contains a phosphorus-containing compound (phosphorus-containing photopolymerizable compound). In this case, a substance obtained by curing the liquid solder resist composition has improved flame retardance. The phosphorus-containing photopolymerizable compound can contain at least one compound selected from the group consisting of 2-methacryloyloxyethylacid phosphate (specific examples include part number “light ester P-1M” and “light ester P-2M” available from Kyoeisha Chemical Co., LTD.), 2-acryloyloxyethylacid phosphate (specific examples include part number “light acrylate P-LA” available from Kyoeisha Chemical Co., LTD.), diphenyl-2-methacryloyloxyethyl phosphate (specific examples include part number “MR-260” available from Daihachi Chemical Co., LTD.), and HFA series available from Showa highpolymer Co., LTD. (specific examples include part number “HFA-6003” and “HFA-6007”, which are products resulting from the addition reaction between dipentaerythritol hexaacrylate and HCA, part number “HFA-3003” and “HFA-6 127”, which are products resulting from the addition reaction between caprolactone modified dipentaerythritol hexaacrylate and HCA, and the like), for example.

Examples of photopolymerizable prepolymers include prepolymers obtained by adding an ethylene-based unsaturated group to a prepolymer obtained by polymerization of a photopolymerizable monomer, oligo (meth)acrylate prepolymers such as epoxy (meth)acrylate, polyester (meth)acrylate, urethane (meth)acrylate, alkyd resin (meth)acrylate, silicone resin (meth)acrylate, and spirane resin (meth)acrylate.

In the present embodiment, the photopolymerization initiator contains bisacylphosphine oxide-based photopolymerization initiator, a first α-hydroxyalkyl phenone-based photopolymerization initiator, and a second α-hydroxyalkyl phenone-based photopolymerization initiator. The first α-hydroxyalkyl phenone-based photopolymerization initiator is a liquid at 25° C., and the second α-hydroxyalkyl phenone-based photopolymerization initiator is a solid at 25° C.

Thus, in the present embodiment, the solder resist layer obtained by curing a coating film made of a liquid solder resist composition using ultraviolet rays can be sufficiently cured entirely from its upper portion to its lower portion. The reason is considered to be as follows.

The bisacylphosphine oxide-based photopolymerization initiator reacts using a component of comparatively long-wavelength ultraviolet rays. Such a component of comparatively long-wavelength is likely to reach the lower portion of the coating film made of the liquid solder resist composition. Therefore, the bisacylphosphine oxide-based photopolymerization initiator can improve the efficiency of a photo-curing reaction in the lower portion of the coating film.

On the other hand, the first α-hydroxyalkyl phenone-based photopolymerization initiator and the second α-hydroxyalkyl phenone-based photopolymerization initiator react using a component having comparatively short-wavelength ultraviolet rays. The component having such comparatively short-wavelength ultraviolet rays is unlikely to reach the lower portion of the coating film. However, the reactions of the first α-hydroxyalkyl phenone-based photopolymerization initiator and the second α-hydroxyalkyl phenone-based photopolymerization initiator are unlikely to be interfered by oxygen, and therefore have high photoreactivity. Therefore, the first α-hydroxyalkyl phenone-based photopolymerization initiator and the second α-hydroxyalkyl phenone-based photopolymerization initiator can improve the efficiency of a photo-curing reaction in the upper portion of the coating film.

Furthermore, because a light wavelength region in which the first α-hydroxyalkyl phenone-based photopolymerization initiator undergoes a reaction is different from a light wavelength region in which the second α-hydroxyalkyl phenone-based photopolymerization initiator undergoes a reaction, ultraviolet rays can be efficiently used. Therefore, the photo-curing reaction further efficiently progresses in the upper portion of the coating film.

Accordingly, in the present embodiment, it is possible to allow the photo-curing reaction to efficiently progress entirely from the upper portion of the coating film to the lower portion thereof. Accordingly, it is conceivable that the upper portion of the solder resist layer can be sufficiently cured and the lower portion thereof can also be sufficiently cured.

If the solder resist layer is sufficiently cured entirely from its upper portion to its lower portion, the degree of hardness of the solder resist layer is unlikely to have variations, as a result of which wrinkles resulting from shrinkage during curing are unlikely to occur in the solder resist layer. Accordingly, the solder resist layer has an improved smoothness.

Also, if the solder resist layer is sufficiently cured from its upper portion to its lower portion, the solder resist layer has an improved homogeneity. Therefore, even though stress occurs due to the solder resist layer being deformed by heat in soldering process, reflowing process, and the like, the stress is easily distributed in the solder resist layer, as a result of which cracks are unlikely to occur in the solder resist layer.

Also, a bisacylphosphine oxide-based photopolymerization initiator is generally likely to be crystallized. If crystals of the bisacylphosphine oxide-based photopolymerization initiator are precipitated in the liquid solder resist composition, there are risks that as a result of the crystals rising to the surface of the coating film made of the liquid solder resist composition, uniformity of the surface of the solder resist layer is deteriorated, reliability of a printed-wiring board is extremely reduced, and it is difficult for the liquid solder resist composition to be uniformly cured using ultraviolet rays. However, in the present embodiment, the liquid solder resist composition contains the first α-hydroxyalkyl phenone-based photopolymerization initiator that is a liquid at 25° C., and thereby crystals of the bisacylphosphine oxide-based photopolymerization initiator are inhibited from being precipitated even though the liquid solder resist composition is stored for a long period of time. Furthermore, the liquid solder resist composition contains the second α-hydroxyalkyl phenone-based photopolymerization initiator that is a solid at 25° C., and thereby the effects are especially obtained. Accordingly, the liquid solder resist composition has an improved storage stability.

Also, if the photopolymerization initiator contains only the bisacylphosphine oxide-based photopolymerization initiator and the first α-hydroxyalkyl phenone-based photopolymerization initiator, the amount of the first α-hydroxyalkyl phenone-based photopolymerization initiator is increased, and thus the tackiness of a coating film (dried coating film) made of the liquid solder resist composition is increased. However, in the present embodiment, the photopolymerization initiator also contains the second α-hydroxyalkyl phenone-based photopolymerization initiator that is a solid at 25° C., and thereby the amount of the first α-hydroxyalkyl phenone-based photopolymerization initiator can be reduced, and the tackiness of the coating film can be reduced without losing a good storage stability. Thus, the coating film can be easily handled, and even though a negative mask or the like is arranged on the coating film when the coating film is exposed to light, the negative mask or the like is unlikely to be attached to the coating film, as a result of which the workability is improved.

Also, the first α-hydroxyalkyl phenone-based photopolymerization initiator and the second α-hydroxyalkyl phenone-based photopolymerization initiator do not generate a benzyl radical at the time of a photo-curing reaction, and therefore the solder resist layer is unlikely to be colored. Furthermore, although the bisacylphosphine oxide-based photopolymerization initiator naturally has a color, bleaching occurs due to decomposition at the time of the photo-curing reaction, as a result of which the solder resist layer is unlikely to be colored. Thus, the solder resist layer is inhibited from turning yellow, whiteness of the solder resist layer is increased, and the good light reflectivity of the solder resist layer can be maintained.

The bisacylphosphine oxide-based photopolymerization initiator can contain at least one component selected from the group consisting of bis-(2,6-dichlorobenzoyl)phenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-2,5-dimethylphenyl phosphine oxide, bis-(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide, bis-(2,6-dimethoxybenzoyl)phenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, bis-(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and (2,5,6-trimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide, for example. In particular, the bisacylphosphine oxide-based photopolymerization initiator preferably contains bis-(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and more preferably contains only bis-(2,4,6-trimethylbenzoyl)phenylphosphine oxide. In these cases, the solder resist layer is further inhibited from being colored.

The melting point of the first α-hydroxyalkyl phenone-based photopolymerization initiator is particularly preferably within a range of −40 to 25° C., and further preferably within a range of 0 to 20° C. The first α-hydroxyalkyl phenone-based photopolymerization initiator can contain at least one of 2-hydroxy-2-methyl-1-phenyl-propane-1-one and phenylglyoxylic acid methyl ester, for example. In particular, the first α-hydroxyalkyl phenone-based photopolymerization initiator preferably contains 2-hydroxy-2-methyl-1-phenyl-propane-1-one, and also preferably contains only 2-hydroxy-2-methyl-1-phenyl-propane-1-one. In these cases, the solder resist layer is further inhibited from being colored.

The melting point of the second α-hydroxyalkyl phenone-based photopolymerization initiator is particularly preferably within a range of 25 to 200° C., and further preferably within a range of 40 to 100° C. The second α-hydroxyalkyl phenone-based photopolymerization initiator can contain at least one component selected from the group consisting of 1-hydroxycyclohexyl phenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one, and 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propane-1-one. In particular, the second α-hydroxyalkyl phenone-based photopolymerization initiator preferably contains 1-hydroxycyclohexyl phenyl ketone, and also preferably contains only 1-hydroxycyclohexyl phenyl ketone. In these cases, the solder resist layer is further inhibited from being colored.

It is preferable that the mass ratio of the bisacylphosphine oxide-based photopolymerization initiator and the first α-hydroxyalkyl phenone-based photopolymerization initiator is within a range of 1:0.5 to 1:5. If the mass ratio of the first α-hydroxyalkyl phenone-based photopolymerization initiator relative to the bisacylphosphine oxide-based photopolymerization initiator is 0.5 or greater, the bisacylphosphine oxide-based photopolymerization initiator is particularly inhibited from being crystallized in the liquid solder resist composition, as a result of which the storage stability of the liquid solder resist composition is increased in particular. Also, if the mass ratio of the first α-hydroxyalkyl phenone-based photopolymerization initiator relative to the bisacylphosphine oxide-based photopolymerization initiator is 5 or less, the tackiness of the coating film (dried coating film) is reduced in particular. It is further preferable that the mass ratio is within a range of 1:1 to 1:4.

It is preferable that the mass ratio of the bisacylphosphine oxide-based photopolymerization initiator and the second α-hydroxyalkyl phenone-based photopolymerization initiator is within a range of 1:0.5 to 1:5. If the mass ratio of the second α-hydroxyalkyl phenone-based photopolymerization initiator relative to the bisacylphosphine oxide-based photopolymerization initiator is 0.5 or greater, dissolution of the bisacylphosphine oxide-based photopolymerization initiator in the liquid solder resist composition is particularly facilitated, as a result of which the storage stability of the liquid solder resist composition is increased in particular. Also, if the mass ratio of the second α-hydroxyalkyl phenone-based photopolymerization initiator relative to the bisacylphosphine oxide-based photopolymerization initiator is 5 or less, the lower portion of the solder resist layer has increased curability. It is further preferable that the mass ratio is within a range of 1:1 to 1:4.

The liquid solder resist composition may further contain a known photopolymerization accelerating agent, a sensitizer, and the like. For example, the liquid solder resist composition may contain p-dimethylbenzoic acid ethyl ester, p-dimethylaminobenzoic acid isoamyl ester, 2-dimethylaminoethyl benzoate, and the like.

It is preferable that the photopolymerization initiator contains only the bisacylphosphine oxide-based photopolymerization initiator, the first α-hydroxyalkyl phenone-based photopolymerization initiator, and the second α-hydroxyalkyl phenone-based photopolymerization initiator. However, the photopolymerization initiator can also contain a component other than three types of the components described above without departing from the gist of the present invention. For example, in addition to the three types of the components described above, the photopolymerization initiator may contain at least one component selected from the group consisting of benzoin and alkyl ethers thereof; acetophenones such as acetophenone and benzyl dimethyl ketal; anthraquinones such as 2-methylanthraquinone; thioxanthones such as 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-isopropyithioxanthone, 4-isopropylthioxanthone, and 2,4-diisopropylthioxanthone; benzophenones such as benzophenone and 4-benzoyl-4′-methyldiphenyl sulfide; xanthones such as 2,4-diisopropyl xanthone; compounds containing a nitrogen atom, such as 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-1-propanone; monoacylphosphine oxide-based photopolymerization initiators such as 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (DAROCUR TPO) and 2,4,6-trimethylbenzoyl-ethyl-phenyl-phosphinate (SPEEDCURE TPO-L); 1,2-octane-dione, 1-[4-(phenylthio)-2-(O-benzoyloxime)] (IRGACURE OXE 01), ethanone and 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]-1-(O-acetyl oxime) (IRGACURE OXE 02).

Titanium dioxide turns the solder resist layer made of the liquid solder resist composition into white, as a result of which it provides the solder resist layer with a high light reflectivity. In the present embodiment, the titanium dioxide contains both of a rutile titanium dioxide manufactured by a sulfuric acid method and a rutile titanium dioxide manufactured by a chlorine method. In a case where only one of the rutile titanium oxides manufactured by the sulfuric acid method or the chlorine method is used, light reflectivity of the solder resist layer may decrease and the solder resist layer may turn its color to yellow due to the ultraviolet rays. However, in a case where the liquid solder resist layer contains both of the rutile titanium dioxides manufactured by two kinds of methods, as in the present embodiment, these two kinds of the rutile titanium oxides can supplement each other's shortcoming with each other's advantage. Therefore, the solder resist layer that has high reflectivity with suppressed deterioration especially due to light can be formed. In other words, since the solder resist layer contains the rutile titanium oxides manufactured by the sulfuric acid method, discoloration such as yellowing of the solder resist layer can be suppressed even if the solder resist layer is irradiated with ultraviolet rays. Moreover, since the solder resist layer contains the rutile titanium oxides manufactured by the chlorine method, b* value in an L*a*b* colorimetric system of the solder resist layer becomes small, which turns the color of the solder resist layer bluish. Due to this, the solder resist layer is likely to be visually recognized as white and thus may have high reflectivity.

The liquid solder resist composition can be made into a thermoset by the compound having a cyclic ether skeleton.

It is particularly preferable that the compound having a cyclic ether skeleton contains an epoxy compound. The compound having a cyclic ether skeleton may be a compound having an oxetane ring.

It is preferable that the epoxy compound has at least two epoxy groups in one molecule. The epoxy compound may be a solvent-insoluble epoxy compound, or a general solvent-soluble epoxy compound. There is no particular limitation on the types of epoxy compounds, and in particular, it is preferable that the epoxy compound contains at least one component selected from the group consisting of phenol novolac epoxy resins (specific examples include part number “EPICLON N-775” available from DIC Corporation), cresol novolac epoxy resins (specific examples include part number “EPICLON N-695” available from DIC Corporation), bisphenol A epoxy resin (specific examples include part number “jER1001” available from Mitsubishi Chemical Corporation), bisphenol A-novolac epoxy resins (specific examples include part number “EPICLON N-865” available from DIC Corporation), bisphenol F epoxy resins (specific examples include part number “jER4004P” available from Mitsubishi Chemical Corporation), bisphenol S epoxy resins (specific examples include part number “EPICLON EXA-1514” available from DIC Corporation), bisphenol AD epoxy resins, biphenyl epoxy resins (specific examples include part number “YX4000” available from Mitsubishi Chemical Corporation), biphenyl novolac epoxy resins (specific examples include part number “NC-3000” available from Nippon Kayaku Co., Ltd.), hydrogenated bisphenol A epoxy resins (specific examples include part number “ST-4000D” available from Nippon Steel & Sumikin Chemical Co., Ltd.), naphthalene epoxy resins (specific examples include part number “EPICLON HP-4032”, “EPICLON HP-4700”, and “EPICLON HP-4770” available from DIC Corporation), hydroquinone-type epoxy resins (specific examples include part number “YDC-1312” available from Nippon Steel & Sumikin Chemical Co., Ltd.), tertiary butylcatechol-type epoxy resins (specific examples include part number “EPICLON HP-820” available from DIC Corporation), dicyclopentadiene type epoxy resins (specific examples include part number “EPICLON HP-7200” available from DIC Corporation), adamantane-type epoxy resins (specific examples include part number “ADAMANTATE X-E-201” available from Idemitsu Kosan Co., Ltd.), biphenyl ether type epoxy resins (specific examples include part number “YSLV-80DE” available from Nippon Steel & Sumikin Chemical Co., Ltd.), unique bifunctional epoxy resins (specific examples include part number “YL7175-500” and “YL7175-1000” available from Mitsubishi Chemical Corporation; part number “EPICLON TSR-960”, “EPICLON TER-601”, “EPICLON TSR-250-80BX”, “EPICLON 1650-75MPX”, “EPICLON EXA-4850”, “EPICLON EXA-4816”, “EPICLON EXA-4822”, and “EPICLON EXA-9726” available from DIC Corporation; part number “YSLV-120TE” available from Nippon Steel & Sumikin Chemical Co., Ltd.), and bisphenol-based epoxy resins other than the epoxy resins described above.

It is also preferable that the epoxy compound contains triglycidyl isocyanurate. As triglycidyl isocyanurate, a β form having three epoxy groups oriented in the same direction relative to a plane of an S-triazine ring skeleton is particularly preferable, and alternatively, a mixture of this β form and an α form that has a structure in which one epoxy group is oriented, relative to a plane of the S-triazine ring skeleton, in a different direction from the direction in which the other two epoxy groups are oriented relative to the plane thereof is preferable.

It is also preferable that the epoxy compound contains a phosphorus-containing epoxy resin. In this case, a substance obtained by curing the liquid solder resist composition has an improved incombustibility. Examples of the phosphorus-containing epoxy resins include a phosphoric acid modified bisphenol F epoxy resin (specific examples include part number “EPICRON EXA-9726” and “EPICLON EXA-9710” available from DIC Corporation) and part number “epotohto FX-305” available from Nippon Steel & Sumikin Chemical Co., Ltd.

The liquid solder resist composition may contain an organic solvent. The organic solvent is used for liquefying or varnishing the liquid solder resist composition, and adjusting the viscosity, application properties, and film formation properties of the liquid solder resist composition, and the like.

The organic solvent can contain at least one compound selected from the group consisting of linear, branched, secondary, or polyhydric alcohols such as ethanol, propyl alcohol, isopropyl alcohol, hexanol, and ethylene glycol; ketones such as methyl ethyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene and xylene; petroleum-based aromatic mixed solvent such as Swazole series (available from Maruzen Petrochemical Co., Ltd.), Solvesso series (available from Exxon Chemical Co.); cellosolves such as cellosolve and butyl cellosolve; carbitols such as carbitol and butyl carbitol; propylene glycol alkyl ethers such as propylene glycol methyl ether; polypropylene glycol alkyl ethers such as dipropylene glycol methyl ether, acetic esters such as ethyl acetate, butyl acetate, cellosolve acetate, and carbitol acetate; and dialkyl glycol ethers, for example.

It is preferable that the ratio of the organic solvent in the liquid solder resist composition is adjusted such that the organic solvent is quickly volatilized when a coating film made of the liquid solder resist composition is dried, or in other words, such that the dried film does not contain the organic solvent. In particular, the organic solvent is preferably within a range of 0 to 99.5% by mass relative to the liquid solder resist composition as a whole, and further preferably within a range of 15 to 60% by mass. It should be noted that it is preferable that the ratio is appropriately adjusted in accordance with an application method because a preferred ratio of the organic solvent is different in accordance with an application method, or the like.

The liquid solder resist composition may further contain a component other than the above-described components without departing from the gist of the present invention.

For example, the liquid solder resist composition may contain at least one resin selected from the group consisting of tolylene diisocyanate-based, morpholine diisocyanate-based, isophorone diisocyanate-based, and hexamethylene diisocyanate-based blocked isocyanates that are blocked with caprolactam, oximes, malonic esters, or the like; amino resins such as melamine resins, n-butylated melamine resins, isobutylated melamine resins, butylated urea resins, butylated melamine-urea co-condensation resins, and benzoguanamine-based co-condensation resins; various types of thermosetting resins other than the above-described resins; ultraviolet-curable epoxy (meth)acrylate; resins obtained by adding (meth)acrylic acid to an epoxy resin such as bisphenol A, phenol novolac, cresol novolac, alicyclic or the like resin; and macromolecular compounds such as diallyl phthalate resins, phenoxy resins, urethane resins, and fluororesins.

In the case where the liquid solder resist composition contains an epoxy compound, the liquid solder resist composition may further contain a curing agent for curing the epoxy compound. The curing agent can contain at least one component selected from the group consisting of imidazole derivatives such as imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 4-phenylimidazole, 1-cyanoethyl-2-phenylimidazole, and 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole; amine compounds such as dicyandiamide, benzyldimethylamine, 4-(dimethylamino)-N,N-dimethylbenzylamine, 4-methoxy-N,N-dimethylbenzylamine, and 4-methyl-N,N-dimethylbenzylamine; hydrazine compounds such as adipic acid hydrazide and sebacic acid hydrazide; phosphorus compounds such as triphenylphosphine; acid anhydrides; phenol; mercaptan; Lewis acid amine complexes; and onium salts, for example. Examples of commercial products of these components include 2MZ-A, 2MZ-OK, 2PHZ, 2P4BHZ, and 2P4MHZ (they are product names of imidazole-based compounds) available from Shikoku Chemicals Corporation, U-CAT3503N and U-CAT3502T (they are product names of blocked isocyanate compounds of dimethylamine), and DBU, DBN, U-CATSA102, and U-CAT5002 (they are bicyclic amidine compounds and salts thereof) available from San-Apro Ltd.

The liquid solder resist composition may contain an adhesion imparting agent. Examples of the adhesion imparting agent include guanamine, acetoguanamine, benzoguanamine, melamine, and S-triazine derivatives such as 2,4-diamino-6-methacryloyloxyethyl-S-triazine, 2-vinyl-4,6-diamino-S-triazine, 2-vinyl-4,6-diamino-S-triazine/isocyanuric acid adducts, and 2,4-diamino-6-methacryloyloxyethyl-S-triazine/isocyanuric acid adducts.

The liquid solder resist composition may contain at least one component selected from the group consisting of hardeners; coloring agents other than white color; copolymers such as silicone and acrylates; leveling agents; adhesion imparting agents such as silane coupling agents; thixotropy agents; polymerization inhibitors; antihalation agents; flame retardants; antifoaming agents; antioxidants; surfactants; macromolecule dispersants; and inorganic fillers such as barium sulfate, crystalline silica, nanosilica, carbon nanotubes, talc, bentonite, aluminum hydroxide, and magnesium hydroxide.

Respective amounts of the components of the liquid solder resist composition are appropriately adjusted such that the liquid solder resist composition has photocurability and can be developed using an alkaline solution.

The percentage of the carboxyl group-containing resin is preferably within a range of 5 to 85% by mass relative to the solid component amount of the liquid solder resist composition, more preferably within a range of 10 to 75% by mass, and further preferably within a range of 10 to 40% by mass.

The percentage of the photopolymerizable compound is preferably within a range of 1 to 45% by mass relative to the solid component amount of the liquid solder resist composition, more preferably within a range of 2 to 40% by mass, and further preferably within a range of 5 to 30% by mass.

Also, the percentage of the compound having a cyclic ether skeleton is preferably within a range of 1.5 to 85% by mass relative to the solid component amount of the liquid solder resist composition, more preferably within a range of 1.5 to 65% by mass, and further preferably within a range of 2 to 40% by mass.

The percentage of the photopolymerization initiator is preferably within a range of 0.1 to 30% by mass relative to the solid component amount of the liquid solder resist composition, and further preferably within a range of 1 to 28% by mass.

Preferable contents of two kinds of the titanium dioxides in the liquid solder resist composition are as follows. It is preferable that relative to 100 parts by mass of a total of the carboxyl group-containing resin, the photopolymerizable compound, and the compound having a cyclic ether skeleton, the rutile titanium dioxide manufactured by the sulfuric acid method is within a range of 30 to 400 parts by mass and the rutile titanium dioxide manufactured by the chlorine method is larger than or equal to 5 parts by mass and less than 50 parts by mass. In this case, light reflectivity of the solder resist layer can be further improved and deterioration due to ultraviolet rays can be further suppressed.

It should be noted that the solid component amount refers to the total amount of all components from which components of solvents and the like that volatilize in the process for forming the solder resist layer from the liquid solder resist composition are removed.

Raw materials for the liquid solder resist composition described above can be mixed and kneaded by a known kneading method using, for example, a three roll mill, a ball mill, or a sand mill to prepare the liquid solder resist composition.

Taking storage stability and the like into consideration, a portion of raw materials for the liquid solder resist composition may be mixed to prepare a first agent, and then a remaining portion of the raw materials may be mixed to prepare a second agent. In other words, the liquid solder resist composition may contain the first agent and the second agent. For example, the photopolymerizable compound, the compound having a cyclic ether skeleton and a portion of the organic solvent, of the raw materials, may be mixed and dispersed in advance to prepare the first agent. Also, the remaining portion of the raw materials may be mixed and dispersed to prepare the second agent. In this case, an appropriate required amount of the first and second agents are mixed at an appropriate time to prepare a liquid mixture, and then the solder resist layer can be formed using this liquid mixture.

The liquid solder resist composition according to the present embodiment is applied for forming the solder resist layer on a printed-wiring board, for example.

Hereinafter, an example of methods for forming the solder resist layer on a printed-wiring board using the liquid solder resist composition according to the present embodiment will be described. In this example, the solder resist layer is formed using a photocurable and thermosetting liquid solder resist composition.

First, a printed-wiring board is prepared, and the liquid solder resist composition is used to form a coating film on the printed-wiring board. For example, the liquid solder resist composition is applied onto the surface of the printed-wiring board to form a wet-state coating film (wet coating film). A method for applying the liquid solder resist composition can be selected from the group consisting of known methods, for example, dipping, spraying, spin coating, roll coating, curtain coating, and screen printing methods. Thereafter, in order to volatilize the organic solvent in the liquid solder resist composition as needed, the wet coating film is dried under a temperature within a range of 60 to 120° C., for example, to obtain a post-dried coating film (dried coating film). In the present embodiment, as a result of the photopolymerization initiator containing three types of components as described above, the tackiness of the dried coating film is suppressed.

It should be noted that when the coating film is formed on the printed-wiring board, it is possible to adopt the following method (dried film method) that: the liquid solder resist composition is applied onto an appropriate support body and then dried to obtain the dried coating film in advance; this dried coating film is placed on the printed-wiring board; and then pressure is applied to the dried coating film and the printed-wiring board to provide the dried coating film on the printed-wiring board.

Thereafter, a negative mask is directly or indirectly applied to the dried coating film on the printed-wiring board, and then the negative mask is irradiated with active energy rays, as a result of which the coating film is exposed to light via the negative mask. The negative mask includes an exposure portion that allows the active energy rays to pass through and a non-exposure portion that blocks the active energy rays, and the exposure portion has a shape that matches the pattern of the solder resist layer. A photo tool such as a mask film or a dry plate is used as the negative mask. The active energy rays are selected in accordance with the composition of the liquid solder resist composition, and in the present embodiment, ultraviolet rays are used. The light source for the ultraviolet rays is selected from the group consisting of a chemical lamp, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a xenon lamp, and a metal halide lamp.

It should be noted that a method other than the method using the negative mask may be adopted as an exposure method. For example, a direct drawing method by means of laser exposure or the like may be adopted.

In the present embodiment, if the dried coating film is exposed to ultraviolet rays in this manner, as described above, a photo-curing reaction efficiently progresses entirely from the upper portion of the dried coating film to the lower portion thereof.

After the dried coating film is exposed to light, the negative mask is removed from the printed-wiring board, and then a development treatment is performed on the dried coating film to remove a portion of the dried coating film that is not exposed to light. As a result, the portion of the dried coating film that was exposed to light remains on a first surface and a second surface of the printed-wiring board as the solder resist layer.

In the development treatment, an appropriate developer can be used in accordance with the composition of the liquid solder resist composition. Specific examples of developers include alkaline solutions such as an aqueous sodium carbonate solution, aqueous potassium carbonate solution, aqueous ammonium carbonate solution, aqueous sodium bicarbonate solution, aqueous potassium bicarbonate solution, aqueous ammonium bicarbonate solution, aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, aqueous ammonium hydroxide solution, aqueous tetramethyl ammonium hydroxide solution, and aqueous lithium hydroxide solution. Organic amines such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, and triisopropanolamine can also be used as the developer. These developers can be used alone or in combination. In the case where the developer is an alkaline solution, the solvent thereof may be only water, or a mixture of water and a hydrophilic organic solvent such as lower alcohols.

The solder resist layer may be heat-cured by performing a heat treatment on the solder resist layer as needed. The conditions for the heat treatment are within a range of a heating temperature of 120 to 180° C. and within a range of a heating time of 30 to 90 minutes, for example. Accordingly, the performance of the solder resist layer, such as the strength, hardness, and chemical resistance, is improved.

Also, after the heat treatment was performed on the solder resist layer, the solder resist layer may be further irradiated with ultraviolet rays as needed. In this case, it is possible to further advance the photo-curing reaction in the solder resist layer. Accordingly, the migration resistance of the solder resist layer is further improved.

As described above, a covered-printed wiring board that includes the printed-wiring board and the solder resist layer that partially covers the printed-wiring board can be obtained. In the present embodiment, the solder resist layer is sufficiently cured entirely from its upper portion to its lower portion. Furthermore, since the solder resist layer contains two kinds of the rutile titanium dioxides manufactured by the sulfuric acid method and the chlorine method, the solder resist layer has high reflectivity and deterioration of the solder resist layer due to light and heat is suppressed.

EXAMPLE

Hereinafter, an example of the present invention will be described. However, the present invention is not limited to the example described below.

[Preparation of Base Resin Solution (Saturated)]

A base resin solution (saturated) containing a carboxyl group-containing resin was prepared as follows.

42 parts by mass of methacrylic acid, 118 parts by mass of methyl methacrylate, 20 parts by mass of N-phenylmaleimide, 20 parts by mass of butyl methacrylate, 320 parts by mass of dipropylene glycol monomethyl ether, and 5 parts by mass of azobisisobutyronitrile were placed in a four-neck flask into which a reflux condenser, a thermometer, a glass tube for nitrogen substitution, and a stirrer were inserted. The liquid in this four-neck flask was heated at 75° C. for 5 hours under nitrogen gas stream to advance a polymerization reaction, as a result of which a copolymer solution having a concentration of 38% was obtained.

[Preparation of Base Resin Solution (Unsaturated)]

A base resin solution (unsaturated) containing a carboxyl group-containing resin was prepared as follows.

60 parts by mass of methacrylic acid, 50 parts by mass of ω-carboxy-polycaprolactone (n≈2) monoacrylate (ARONIX M-5300 available from Toagosei Co., LTD.), 80 parts by mass of methyl methacrylate, 10 parts by mass of styrene, 430 parts by mass of dipropylene glycol monomethyl ether, and 5 parts by mass of azobisisobutyronitrile were placed in a four-neck flask into which a reflux condenser, a thermometer, a glass tube for nitrogen substitution, and a stirrer were inserted. The liquid in this four-neck flask was heated at 75° C. for 5 hours under nitrogen gas stream to advance a polymerization reaction, as a result of which a copolymer solution having a concentration of 32% was obtained.

0.1 parts by mass of hydroquinone, 64 parts by mass of glycidylmethacrylate, and 0.8 parts by mass of dimethylbenzylamine were added to this copolymer solution, and the mixture was heated at 80° C. for 24 hours to advance an addition reaction. Accordingly, a 38% solution of a compound having a carboxyl group and an ethylene-based unsaturated group was obtained.

[Preparation of Liquid Solder Resist Compositions]

Liquid solder resist compositions were each obtained by mixing components in accordance with an item in Tables below and kneaded using a three roll mill. It should be noted that the details of the components shown in Table are as follows.

-   -   Photopolymerization initiator (IRGACURE819);         bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, available         from BASF SE, part number “IRGACURE819”.     -   Photopolymerization initiator (IRGACURE184);         1-hydroxy-cyclohexyl-phenyl-ketone, available from BASF SE, part         number “IRGACURE 184”.     -   Photopolymerization initiator (DAROCUR 1173);         2-hydroxy-2-methyl-1-phenyl-propane-1-one, available from BASF         SE, part number “DAROCUR 1173”.     -   Rutile titanium dioxide R-79; a rutile titanium dioxide         manufactured by the sulfuric acid method, available from Sakai         Chemical Industry Co., Ltd., part number “R-79”.     -   Rutile titanium dioxide D-918; a rutile titanium dioxide         manufactured by the sulfuric acid method, available from Sakai         Chemical Industry Co., Ltd., part number “D-918”.     -   Rutile titanium dioxide CR-90; a rutile titanium dioxide         manufactured by the chlorine method, available from Ishihara         Sangyo Kaisha, LTD, part number “CR-90”.     -   Rutile titanium dioxide CR-58; a rutile titanium dioxide         manufactured by the chlorine method, available from Ishihara         Sangyo Kaisha, LTD, part number “CR-58”.     -   Anatase titanium dioxide A-100; available from Ishihara Sangyo         Kaisha, LTD, part number “A-100”.     -   Epoxy compound; available from Nissan Chemical Industries, Ltd.,         part number “TEPIC-SP”.     -   Organic solvent; Methyl Propylene Di Glycol, available from         Nippon Nyukazai Co., Ltd., part number “MFDG”.     -   Photopolymerizable monomer; available from Nippon Kayaku Co.,         Ltd., part number “KAYARAD DPCA-20”.     -   Antifoaming agent; available from Shin-Etsu Chemical Co., Ltd.,         part number “KS-66”.     -   Melamine; available from Nissan Chemical Industries, Ltd., fine         powder melamine.     -   Antioxidant; available from BASF SE, part number “IRGANOX 1010”.

[Evaluation Test]

(1) Production of Test Pieces

A glass epoxy copper clad laminate that includes a copper foil having a thickness of 35 μm was prepared. Etching was performed on this glass epoxy copper clad laminate to form conductive wiring, as a result of which a printed-wiring board was obtained. A liquid solder resist resin composition was applied to the entire surface of the printed-wiring board by screen printing, as a result of which a coating film was formed. This coating film was heated at 80° C. for 20 minutes to be dried. The thickness of a coating film obtained after drying the coating film (dried coating film) was 20 μm. While a negative mask was directly applied to the surface of the dried coating film, the negative mask was irradiated with ultraviolet rays so that the dried coating film was selectively exposed to light under the condition of an exposure energy of 450 mJ/cm². Subsequently, after the negative mask was removed from the dried coating film, the development treatment was performed on the dried coating film using an aqueous sodium carbonate solution, as a result of which a portion of the dried coating film that was cured by light exposure was left on the printed-wiring board as a solder resist layer. This solder resist layer was further heated at 150° C. for 60 minutes to be cured by heat. According to such procedures, test pieces 1 that each included the solder resist layer with thickness of 20 μm were obtained. Besides, the liquid solder resist resin composition was applied by screen printing on a surface of the dried coating film of another printed wiring board before the above ultraviolet rays irradiation, as a result of which a coating film was formed. The coating film was dried by heating for 20 minutes at 80° C. The post-dried coating film (dried coating film) had a thickness of 40 μm. Similar processes as described above but with a different exposure energy of 600 mJ/cm² were performed thereon, as a result of which test pieces 2 that each included the solder resist layer with thickness of 40 μm were obtained.

The following evaluation tests were performed on these test pieces 1, 2.

(2) Evaluation of Adhesion

In accordance with a test method of JIS D0202, a cross-cut was made into the solder resist layer of each test piece 1, and then the peeled state after a peeling test using the cellophane adhesive tape was visually observed. The results were evaluated as follows.

A: there was no change in all of the 100 cross-cut portions.

B: there was a slight raise in one portion among the 100 cross-cut portions.

C: there was peeling from 2 to 10 portions among the 100 cross-cut portions.

D: there was peeling from 11 to 100 portions among the 100 cross-cut portions.

(3) Pencil Hardness

The pencil hardness of the solder resist layer of each test piece 1 was measured using a Mitsubishi Hi-uni pencil (available from Mitsubishi Pencil Co., Ltd.) in accordance with JIS K5400.

(4) Evaluation of Reflectivity

Y value in an CIE colorimetric system, which expresses a luminous reflectance, of the solder resist layer of each test piece 1 and test piece 2 before a discoloration test was measured using a spectrophotometer (model number “CM-600d”) available from Konica Minolta Sensing, Inc. Then, after the discoloration test was carried out by irradiating the solder resist layer of each test piece 1 and test piece 2 with ultraviolet rays (UV) under the condition of 50 J/cm², Y value of the solder resist layer was again measured using the same method as above.

(5) Evaluation of Yellowing Resistance Due to Ultraviolet Rays

b* value in an L*a*b* colorimetric system of the solder resist layer of each test piece 1 and test piece 2 before a discoloration test was measured using a spectrophotometer (model number “CM-600d”) available from Konica Minolta Sensing, Inc. Then, after the discoloration test was carried out by irradiating the solder resist layer of each test piece 1 and test piece 2 with ultraviolet rays (UV) under the condition of 50 J/cm², b* value of the solder resist layer was again measured using the same method as above. A value (Δb*) was calculated by subtracting the b* value of the solder resist layer before the UV irradiation from the b* value of the solder resist layer after the UV irradiation. In addition, a surface of the solder resist layer after the UV irradiation was visually observed and the results were evaluated as follows.

A: there was no particularly large change in luster on the surface of the solder resist layer.

B: there was a slight decrease in luster on the surface of the solder resist layer.

C: there was no luster on the surface of the solder resist layer.

TABLE 1 Examples Comperative Examples 1 2 3 4 5 6 7 8 9 10 1 2 3 4 Composition/ base resin solution (saturated) 100 100 100 100 100 100 100 100 100 100 100 100 parts by mass base resin solution (unsaturated) 100 100 photopolymerization initiator 5 5 6 5 4 5 6 5 4 4 5 5 5 5 (IRGACURE819) photopolymerization initiator 8 8 5 8 6 8 5 8 6 6 8 8 8 8 (IRGACURE184) photopolymerization initiator 13 13 12 13 10 13 12 13 10 10 13 13 13 13 (DAROCUR1173) titanium dioxide (R-79) 85 70 55 55 55 115 145 70 55 100 titanium dioxide (D-918) 55 titanium dioxide (CR-90) 15 30 45 45 45 45 15 30 45 45 100 titanium dioxide (CR-58) 100 titanium dioxide (A-100) 100 epoxy compound 10 10 10 10 10 10 10 10 10 10 10 10 10 10 organic solvent 10 10 10 10 10 20 20 5 5 10 10 10 10 10 photopolymerizable 30 30 30 30 30 40 40 20 20 30 30 30 30 30 monomer (DPCA-20) antifoaming agent 1 1 1 1 1 1 1 1 1 1 1 1 1 1 melamine 2 2 2 2 2 2 2 2 2 2 2 2 2 2 antioxidant 1 1 1 1 1 1 1 1 1 1 1 1 1 1 adhesion A A A A A A A A A A A A A A pencil hardness 5H 5H 5H 5H 5H 5H 5H 5H 5H 5H 5H 5H 5H 5H reflectivity (Y value) before the 85 85 85 85 85 86 85 85 85 85 83 85 75 82 discoloration test (%) (20 μm) reflectivity (Y value) after the 84 84 84 84 84 85 84 84 84 85 82 83 65 80 discoloration test (%) (UV irradiation) (20 μm) b* value before the discoloration 2 2 1.9 1.9 1.9 2 2.1 2 1.9 2.5 2.6 1.9 3 1.7 test (20 μm) Δb* after the discoloration test 0.6 0.6 0.7 0.7 0.7 0.6 0.6 0.6 0.7 0.3 0.7 1.0 10 1.2 (UV irration) (20 μm) visual evaluation after the A A A A A A A A A A A B C B discoloration test (UV irradiation) (20 μm) reflectivity (Y value) before the 90 90 90 90 90 90 90 90 90 90 88 90 79 85 discoloration test (%) (40 μm) reflectivity (Y value) after the 88 88 88 88 88 88 88 88 88 89 86 86 68 80 discoloration test (%) (UV irradiation) (40 μm) b* value before the discoloration 2.3 2.3 2.2 2.2 2.2 2.3 2.4 2.3 2.2 2.8 3 2.2 3.3 1.9 test (40 μm) Δb* after the discoloration test 0.7 0.7 0.8 0.8 0.8 0.7 0.7 0.7 0.8 0.4 0.7 2.2 12 2.8 (UV irradiation) (40 μm) visual evaluation after the A A A A A A A A A A A B C B discoloration test (UV irradiation) (40 μm) 

1. A liquid solder resist composition comprising: a carboxyl group-containing resin; a photopolymerizable compound containing at least one compound selected from a group consisting of a photopolymerizable monomer and a photopolymerizable prepolymer; a photopolymerization initiator; a titanium dioxide; and a compound having a cyclic ether skeleton, the titanium dioxide containing both of a rutile titanium dioxide manufactured by a sulfuric acid method and a rutile titanium dioxide manufactured by a chlorine method, the rutile titanium dioxide manufactured by the sulfuric acid method being within a range of 30 to 400 parts by mass relative to 100 parts by mass of a total of the carboxyl group-containing resin, the photopolymerizable compound, and the compound having a cyclic ether skeleton, and the rutile titanium dioxide manufactured by the chlorine method being larger than or equal to 5 parts by mass and less than 50 parts by mass, relative to 100 parts by mass of a total of the carboxyl group-containing resin, the photopolymerizable compound, and the compound having a cyclic ether skeleton.
 2. (canceled)
 3. The liquid solder resist composition according to claim 1, wherein the photopolymerization initiator contains a bisacylphosphine oxide-based photopolymerization initiator, a first α-hydroxyalkyl phenone-based photopolymerization initiator, and a second α-hydroxyalkyl phenone-based photopolymerization initiator.
 4. The liquid solder resist composition according to claim 3, wherein: the bisacylphosphine oxide-based photopolymerization initiator contains bis-(2,4,6-trimethylbenzoyl)phenylphosphine oxide; the first α-hydroxyalkyl phenone-based photopolymerization initiator contains 2-hydroxy-2-methyl-1-phenyl-propane-1-one; and the second α-hydroxyalkyl phenone-based photopolymerization initiator contains 1-hydroxycyclohexyl phenyl ketone.
 5. The liquid solder resist composition according to claim 3, wherein a mass ratio of the bisacylphosphine oxide-based photopolymerization initiator and the first α-hydroxyalkyl phenone-based photopolymerization initiator is within a range of 1:0.5 to 1:5.
 6. The liquid solder resist composition according to claim 3, wherein a mass ratio of the bisacylphosphine oxide-based photopolymerization initiator and the second α-hydroxyalkyl phenone-based photopolymerization initiator is within a range of 1:0.5 to 1:5.
 7. The liquid solder resist composition according to claim 1, wherein the carboxyl group-containing resin contains a photopolymerizable carboxyl group-containing resin having a carboxyl group and a photopolymerizable functional group.
 8. The liquid solder resist composition according to claim 7, wherein the photopolymerizable carboxyl group-containing resin contains a carboxyl group-containing (meth)acrylic copolymer resin.
 9. A covered-printed wiring board, comprising a printed-wiring board and a solder resist layer that covers the printed-wiring board, wherein the solder resist layer is made of the liquid solder resist composition according to claim
 1. 10. The liquid solder resist composition according to claim 1, wherein: a percentage of the carboxyl group-containing resin is within a range of 5 to 85% by mass relative to a solid component amount of the liquid solder resist composition; a percentage of the photopolymerizable compound is within a range of 1 to 45% by mass relative to the solid component amount of the liquid solder resist composition; and a percentage of the compound having a cyclic ether skeleton is within a range of 1.5 to 85% by mass relative to the solid component amount of the liquid solder resist composition.
 11. The liquid solder resist composition according to claim 1, wherein a percentage of the photopolymerization initiator is within a range of 0.1 to 30% by mass relative to the solid component amount of the liquid solder resist composition. 